The invention relates to a power distribution system in the low-voltage range, in particular, in the 24V DC range, having a number of circuits each having an electronic circuit breaker as a short-circuit and/or overload protection.
Such a power distribution system is disclosed, for example, by German Published, Non-Prosecuted Patent Application DE 197 03 236 A1, corresponding to U.S. Pat. No. 6,157,089 to Xu.
In a power distribution or power supply system having a plurality of circuits fed jointly by a low-voltage power supply unit, high requirements are placed on operational reliability. In the main application of plant construction, there are loads, for example, in the form of actuators or sensors, in the circuits or current paths that are connected in parallel with one another and fed jointly by the power supply unit. In such a case, a mechanical circuit breaker, possibly a switching element (relay) and the actual load or the actuator or the sensor is usually disposed one behind another in each circuit or stream. The mechanical circuit breaker can operate in accordance with a thermal or in accordance with a thermal and a magnetic disconnection characteristic.
In a linearly controlled power supply unit or transformer power supply unit, usually employed in practice to supply power (having a rated current of, for example, 30 A and a short-circuit current of about 300 A) in the event of a short circuit, it is ensured, within an individual circuit, for example, that the fuse in the circuit also triggers. The reason for such is that the short-circuit current is always sufficiently high (for example, 100 A) to trigger the circuit breaker quickly enough. In addition, for the conventional case, in which twenty or more circuits are supplied simultaneously by such a single power supply unit, it is additionally ensured that, in the aforementioned short-circuit case, the output voltage supplied by the linear or linearly controlled power supply unit does not break down or breaks down only to an insignificant extent. As is also the case in the on-board controller for a motor vehicle disclosed by Xu, the aforementioned means that the circuits that are not affected continue to be supplied with the necessary power without disruption and, in particular, in a functionally reliable manner.
The behavior is different in the case of clocked power supply units that, on account of their comparatively small dimensions, are to be employed increasingly for the aforementioned application in plant construction. These clocked power supply units likewise supply the desired output voltage of, for example, 24 VDC, but only a short-circuit current of, for example, 33 A. The latter is, therefore, frequently only 10% higher than the rated current of the clocked power supply unit of, for example, 30 A. As opposed to the linearly controlled power supply unit, in the case of a clocked power supply unit it is not ensured that, in the event of a short circuit, that is to say, in the event of a short circuit within an individual circuit downstream of the circuit breaker, the latter also triggers reliably. The reason is because the clocked power supply unit, which protects itself by limiting its output, controls the voltage down appropriately or, in the case of long load lines, the short-circuit current necessary for triggering cannot flow because of the purely resistive line component.
In the extreme case, that is to say, also in the case of a short circuit in only one circuit, it is, therefore, possible for the output voltage from the clocked power supply unit, and, therefore, the supply voltage for the parallel circuits, to be controlled down at least approximately to zero volts (0 V). As such, virtually no (short-circuit) current flows through the actual circuit breaker in the relevant circuit. At the least, however, the latter is often too small to trigger the mechanical circuit breaker. A conventional circuit breaker as fuse in the relevant circuit may, therefore, trigger only thermally. However, this means that the triggering of such a circuit breaker, on account of the conventional thermal characteristic, only takes place after 20 sec, for example. During such time, the supply voltage is too low for the other circuits or current paths to ensure their reliable operation (power reset). Therefore, the entire part of the plant that is supplied by the clocked power supply unit is disrupted and, accordingly, no longer serviceable. In other words, in the event of a short circuit, even in only one individual circuit or current path, there is a reaction on the other, intact circuits, as a result of which the intact circuits are likewise disrupted. Operational reliability is, therefore, not reliably ensured. This is because there is no assurance that, in the event of a short circuit or else circuits an overload, the other in parallel with the affected circuit and likewise supplied by the clocked power supply unit will receive the necessary power, if the clocked power supply unit controls down its output and, therefore, the supply voltage.
Because, in addition, the mechanical circuit breaker in the affected circuit does not trigger, or triggers only with an extreme delay, it is virtually impossible to determine which circuit is affected, particularly because the other circuits are also disrupted due to the reaction. If xe2x80x9cpower-fail resetsxe2x80x9d are incorporated in the individual circuits or current paths, then all the circuits shut down in such a xe2x80x9cworst case.xe2x80x9d If no such reset is incorporated, then the power in the further, intrinsically intact streams is in any case so low that the loads, in particular, the actuators or sensors, can no longer operate without faults.
It is accordingly an object of the invention to provide a power distribution system that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has a plurality of circuits supplied jointly by a clocked power supply unit in which the aforementioned disadvantages are avoided and ensures a high operational reliability of the overall system. In particular, a suitable protective device is supplied for such a power distribution system.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a power distribution system includes circuits each having an electronic circuit breaker as a protection for at least one of short-circuits and overloads, and a clocked power supply unit connected to the circuits and feeding power to the circuits. In particular, the power distribution system is in the 24V DC range. The electronic circuit breaker has a power stage and an adjustable current limiting device connected to the power stage. The adjustable current limiting device, in the event of an overload and when a first adjustable current threshold is exceeded, turns off the power stage after a first adjustable disconnection time has expired, and in the event of a short circuit and after a second adjustable current threshold has been exceeded, turns off the power stage after a second disconnection time has expired.
According to the invention, an electronic circuit breaker is inserted into each of the circuits supplied by the clocked power supply unit in the power distribution system. The circuit breaker is used substantially to limit the current within the circuit affected by short circuit and/or overload. In such a case, the current limiting device is advantageously adjustable, that is to say, can be regulated or controlled actively.
For such a purpose, the electronic circuit breaker expediently includes a power stage, preferably, in the form of a semiconductor, for example, a power MOS transistor, which is turned on completely in the normal state, that is to say, with an intended load current in the respective circuit.
In accordance with another feature of the invention, the adjustable current limiting device is programmed to turn off the power stage after a first adjustable disconnection time has expired in the event of an overload and when a first adjustable current threshold is exceeded, and programmed to turn off the power stage after a second disconnection time has expired in the event of a short circuit and after a second adjustable current threshold has been exceeded.
In accordance with a further feature of the invention, the adjustable current limiting device has a means for turning off the power stage after a first adjustable disconnection time has expired in the event of an overload and when a first adjustable current threshold is exceeded, and a means for turning off the power stage after a second disconnection time has expired in the event of a short circuit and after a second adjustable current threshold has been exceeded.
In accordance with an added feature of the invention, the electronic circuit breaker has a measured-value registration part for measuring a load current flowing in a corresponding one of the circuits, and a control stage adjusting current limiting of the power stage and turning the power stage off as a function of time, the control stage connected to the power stage and the measured-value registration part.
The measured, value registration part is, for example, a shunt, with which, in particular, the load current flowing through the respective circuit is registered. Also provided is a control stage that, by using the registered load current and, preferably, by using the voltage across the load stage, that is to say, the voltage drop across the semiconductor, supplies an appropriate control signal for the power stage.
In the event of an overload, for example, in the range of 105% to 200% of the rated current of the load stage, and, therefore, in the event that a first adjustable current threshold is exceeded, a timer expires. The time expiry can be, for example, 1 sec to 20 sec, in particular, 5 sec, which corresponds to the thermal characteristic of a conventional circuit breaker. After the timer has expired, the power circuit breaker, that is to say, the power stage, is switched off. In the case of a semiconductor, this means that it is turned off and can be turned on again only by a reset.
In accordance with an additional feature of the invention, the adjustable current limiting device electromagnetically isolates a relevant one of the circuits from the power supply unit in the event of one of the group consisting of a short circuit and an overload. The isolation can be done by a controllable triggering relay with additional indicator, which is then activated appropriately by the control stage and isolates the affected circuit electromechanically from the power supply unit. To perform the isolation, in accordance with yet another feature of the invention, the adjustable current limiting device is programmed to electromagnetically isolate a relevant one of the circuits from the power supply unit in the event of one of the group consisting of a short circuit and an overload. Alternatively, in accordance with n yet a further feature of the invention, the adjustable current limiting device has a means for electromagnetically isolating a relevant one of the circuits from the power supply unit in the event of one of the group consisting of a short circuit and an overload.
In the event of a short circuit, in theory, the short-circuit current would exceed a predefinable second current threshold, which, for example, is 200% of the rated current of the power stage. However, the current flowing through the affected circuit will be (current) limited to preferably 200% of the rated current, that is to say, to twice the rated current of the power stage. Current limitation can also be carried out, for example, at more or less than 200% of the rated current.
In the event of a short circuit, therefore, the magnetic characteristic of a conventional circuit breaker will be simulated. In addition, the voltage across the power stage and, therefore, the voltage drop across the switched-on semiconductor can be registered. The voltage value across the power stage specifies the disconnection rate, that is to say, after the expiry of what time the semiconductor will be turned off. If, for example, only a small part of the supply voltage from the clocked power supply unit is present across the semiconductor, then disconnection will take place, for example, only after 500 ms. If, on the other hand, the entire power supply voltage is across the semiconductor, then disconnection will take place after, for example, at most 5 ms.
The advantages achieved by the invention reside, in particular, in the fact that when a clocked power supply unit is used for the simultaneous supply of a large number of circuits connected in parallel to the output side of the clocked power supply unit, high operational reliability of the corresponding power distribution system is ensured by the use of electronic circuit breakers in each circuit. At the same time, in the event of an overload and/or short circuit in one of the circuits fed, adequate line protection in the circuit is ensured and the other circuits are supplied with, if possible, an undiminished output. In the event of a short circuit and/or overload, the output voltage from the clocked power supply unit, and, therefore, the supply voltage for the intact circuits, does not fall or falls only to an insignificant extent below the nominal or intended voltage. In particular, in the event of a short circuit in a circuit, first of all current limitation over the affected circuit is carried out reliably, so that the output voltage of the clocked power supply unit is at least virtually completely maintained.
By the use of such electronic circuit breakers in each of the parallel circuits supplied jointly by the clocked power supply unit, virtually reaction-free short-circuit and/or overload protection of the entire power distribution system is ensured. The reason for the effect is that, even in the event of failure of a circuit, the electronic circuit breaker, by virtue of the actively controlled current limitation in the circuit, ensures that the other circuits are not affected to the extent that the output voltage from the clocked power supply unit is maintained virtually unchanged. The circuit breaking device having a number of electronic circuit breakers corresponding to the number of circuits supplied jointly by a clocked power supply unit is, therefore, particularly suitable for power or current distribution in the 24 V DC range, whose classic application is in plant construction, in particular, in the automobile industry.
In accordance with a concomitant feature of the invention, at least one of the circuits has a fail-safe element for redundant line protection and/or reverse polarity protection. The fail-safe element can be connected to the power stage and/or the control stage.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a power distribution system, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.